fix(api): alloc and draw cursor window in nvim__redraw

Problem:  Unable to move cursor to recently opened window.
Solution: Make sure uninitialized window is drawn before trying to move
          the cursor to it.

src/nvim/api/vim.c

@@ -2393,10 +2393,6 @@ void nvim__redraw(Dict(redraw) *opts, Error *err)
     redraw_buf_range_later(rbuf, first, last);
   }
 
-  if (opts->cursor) {
-    setcursor_mayforce(win ? win : curwin, true);
-  }
-
   bool flush = opts->flush;
   if (opts->tabline) {
     // Flush later in case tabline was just hidden or shown for the first time.
@@ -2423,11 +2419,22 @@ void nvim__redraw(Dict(redraw) *opts, Error *err)
     }
   }
 
-  // Flush pending screen updates if "flush" or "clear" is true, or when
+  win_T *cwin = win ? win : curwin;
-  // redrawing a status component may have changed the grid dimensions.
+  // Allow moving cursor to recently opened window and make sure it is drawn #28868.
+  if (opts->cursor && (!cwin->w_grid.target || !cwin->w_grid.target->valid)) {
+    flush = true;
+  }
+
+  // Redraw pending screen updates when explicitly requested or when determined
+  // that it is necessary to properly draw other requested components.
   if (flush && !cmdpreview) {
     update_screen();
   }
+
+  if (opts->cursor) {
+    setcursor_mayforce(cwin, true);
+  }
+
   ui_flush();
 
   RedrawingDisabled = save_rd;

test/functional/api/vim_spec.lua

@@ -4969,12 +4969,29 @@ describe('API', function()
   it('nvim__redraw', function()
     local screen = Screen.new(60, 5)
     screen:attach()
-    local win = api.nvim_get_current_win()
     eq('at least one action required', pcall_err(api.nvim__redraw, {}))
     eq('at least one action required', pcall_err(api.nvim__redraw, { buf = 0 }))
     eq('at least one action required', pcall_err(api.nvim__redraw, { win = 0 }))
     eq("cannot use both 'buf' and 'win'", pcall_err(api.nvim__redraw, { buf = 0, win = 0 }))
+    local win = api.nvim_get_current_win()
+    -- Can move cursor to recently opened window and window is flushed #28868
     feed(':echo getchar()<CR>')
+    local newwin = api.nvim_open_win(0, false, {
+      relative = 'editor',
+      width = 1,
+      height = 1,
+      row = 1,
+      col = 10,
+    })
+    api.nvim__redraw({ win = newwin, cursor = true })
+    screen:expect({
+      grid = [[
+                                                                    |
+        {1:~         }{4:^ }{1:                                                 }|
+        {1:~                                                           }|*2
+        :echo getchar()                                             |
+      ]],
+    })
     fn.setline(1, 'foobar')
     command('vnew')
     fn.setline(1, 'foobaz')
@@ -4983,11 +5000,13 @@ describe('API', function()
     screen:expect({
       grid = [[
         foobaz                        │foobar                       |
-        {1:~                             }│{1:~                            }|*2
+        {1:~         }{4:^f}{1:                   }│{1:~                            }|
+        {1:~                             }│{1:~                            }|
         {3:[No Name] [+]                  }{2:[No Name] [+]                }|
-        ^:echo getchar()                                             |
+        :echo getchar()                                             |
       ]],
     })
+    api.nvim_win_close(newwin, true)
     -- Can update the grid cursor position #20793
     api.nvim__redraw({ cursor = true })
     screen:expect({